The invention relates to the cooling of airfoils of a gas-turbine engine and particularly to an improved method and apparatus for making the same.
U.S. Pat. No. 4,197,443 is descriptive of the purpose and current practice for making cooling holes in turbine blades of the character indicated, wherein the airfoil is hollow and is supplied with cooling air under high pressure, and wherein the cooling holes distribute the cooling air over the active surface of the airfoil, via a diffuser formation extending laterally and downstream from the discharge end of each of a plurality of the cooling holes. The particular technique of said patent involves electric-discharge machining (EDM) wherein a single electrode is so configurated as to form both the cooling hole and its diffusion area; the disclosure of the patent also teaches that a single such electrode may comprise comb-like formations whereby a single EDM-machining stroke may develop and form both the hole and the diffuser for each of an arrayed plurality of holes and associated diffusers in a single blade.
Although the indicated method and apparatus produce reliably uniform products, the process consumes excessive time and is therefore relatively expensive.